As means for sharing data in a centralized storage resource among a plurality of clients, a remote file access service through a de facto standard protocol such as NFS (Network File System) or CIFS (Common Internet File System) can be pointed out. As server devices that use the protocol, there are NAS (Network Attached Storage), a file server, and the like. Using the above mentioned protocol, connection with various clients has become possible.
A common feature of these devices is that these devices do not have a standardized mechanism for performing interconnection among a plurality of the devices to make mutual access to one another's storage resources of the devices, so that file access service provided to a client is limited to storage resources managed by NAS or the server itself.
In Patent Documents 1 and 2, there are disclosed a system in which a switch is introduced into a network between a client and a file server such as NAS a switch device. The switch has a function of changing part of information in a packet to transfer the packet using interpretation of the industrial standard file access protocol such as NFS and CFS. The system is equipped with a function of providing to the client a plurality of server storage resources as if they were one storage resource without introducing special software and hardware into the client and the server. Further, by using the function of data migration (rearrangement) between the servers, reduction of a management operation such as addition of the file server or replacement has become possible.
As other means for sharing the data in the centralized storage resource among the clients, service of providing contents dedicated for reading only by a Web server or the like can be pointed out. Generally, in the provision of data on the contents by the Web server, data reading by the client in a remote place has also become possible through the Internet. Normally, compared with a case where data in a local area is accessed, its response time is longer. Then, an approach is employed in which by arranging a cache server for temporarily storing data once accessed by the client in the vicinity of the installed location of the client, high-speed data reading comparable to that of the data disposed in the local area can be implemented by the client, and a delay resulting from an access to data in the remote place is reduced.
[Patent Document 1]
JP Patent Kokai Publication No. JP-P-2003-203029A
[Patent Document 2]
JP Patent Kokai Publication No. JP-P-2004-54607A